1. Field of the Invention
The present invention relates to golf balls. More particularly, the present invention relates to multi-piece golf balls having a center, a mid layer, an inner cover and an outer cover.
2. Description of the Related Art
Golf players' greatest demand for golf balls is flight performance. Golf players emphasize flight performance with a driver, a long iron and a middle iron. The flight performance is correlated with the resilience performance of the golf ball. When the golf ball excellent in resilience performance is hit, the golf ball flies at a fast speed to accomplish great flight distance. The flight performance is further correlated with spin rate. The golf ball flies at a small spin rate, thereby obtaining proper trajectory to accomplish great flight distance. In light of flight performance, golf balls which have high resilience performance and are not likely to be spun are desired. Golf players further emphasize feel at impact. Golf players prefer soft feel at impact.
Further, golf players emphasize also spin performance of golf balls. If a backspin rate is high, the run is short. By using a golf ball which has a high backspin rate, golf players can let the golf ball to stop at a target point. By using a golf ball which has a high sidespin rate, golf players can intentionally let the golf ball to curve. A golf ball with excellent spin performance has excellent controllability. In particular, high-level golf players place importance on controllability of a shot with a short iron.
A variety of golf balls having a multi-layer structure have been proposed. U.S. Pat. No. 6,468,169 (JP-A-10-328326) discloses a golf ball having an inner core, a surrounding layer, an inner cover and an outer cover. U.S. Pat. No. 6,271,296 (JP-A-2001-17575) discloses a golf ball having a core, a surrounding layer, a middle layer and a cover. JP-A-2002-272880 discloses a golf ball having a core and a cover. The core has a center and an outer core layer. The cover has an inner cover layer and an outer cover layer. US2003/166422 (JP-A-2003-205052) discloses a golf ball having a center, a mid layer and a cover. US2004/29648 (JP-A-2004-130072) discloses a golf ball having a core and a cover. The core has a three-layered construction.
When a golf ball has an outer-hard/inner-soft structure, the spin upon a shot with a driver may be suppressed. The conventional golf ball uses a soft center, a hard mid layer and a hard cover in order to attain the outer-hard/inner-soft structure. In this golf ball, the hardness distribution up to the central point of a center from the surface of a mid layer has a large level difference on the boundary of the center and the mid layer. This level difference deteriorates the suppression of spin. A soft center deteriorates the resilience performance. A hard cover deteriorates feel at impact. Further, the hard cover deteriorates controllability upon a shot with a short iron.
Golf players' demand to the golf ball has been increasingly escalating. It is an object of the present invention to provide a golf ball excellent in various performances.